Conventional rolling lines of steel rods, wires, and the like manufacture the products by rolling steel pieces such as blooms and billets one by one. In recent years, however, there has been proposed a technology of preventing the reduction of product yield resulting from cutting to remove the crops of leading and trailing ends of steel pieces and improving productivity by eliminating idle time between steel pieces. According to that technology, pluralities of steel pieces delivered from a heating furnace or directly fed from a continuous casting machine are welded with each other while traveling by a traveling flash welding machine at an upstream side of the rolling mill train or in the rolling mill train to form an endless steel piece. Thus formed endless steel piece is continuously rolled as disclosed in Japanese Patent Publication Nos. 52-43754 and 9-66301.
During the operation of the above technology, the welded parts of steel pieces which were joined together by flash welding form welding burrs. Since the welding burrs are relatively large, they generate flaws in the succeeding rolling step to decrease the product yield, and they may cause a break or the like in the rolling step. Consequently, those welding burrs have to be removed before rolling after the welding.
There is a known deburring machine to remove welding burrs from flash welded parts, which is a deburring machine built in a traveling flash welding machine. FIG. 12 shows a continuous rolling apparatus provided with that type of deburring machine, and FIG. 13 shows a perspective view of a core part of that deburring machine.
In FIG. 12, the rolling line has a heating furnace 10, a traveling flash welding machine 20, and a rolling mill 60, in sequential order. The traveling flash welding machine 20 has a deburring machine 30. As illustrated in FIG. 13, the deburring machine 30 is equipped with a vertical deburring cutter 31 in a downward-opening angular U-shape, a hydraulic cylinder 32 to drive the vertical deburring cutter 31 in the vertical directions, a horizontal deburring cutter 33 in a side-opening angular U-shape, and a hydraulic cylinder 34 to drive the horizontal deburring cutter 33 in the horizontal directions. The reference numbers 21a and 22b in FIG. 13 signify welding clamps to conduct flash welding while clamping to upset a preceding billet 1a and a succeeding billet 1b, respectively.
In such a structured rolling line, the leading end of the succeeding billet 1b delivered from the heating furnace 10 and the trailing end of the preceding billet 1a are welded together by the traveling flash welding machine 20, and welding burrs 2 formed on the welded part are removed by the deburring machine 30. Then, thus formed endless billet 1 is continuously rolled by the rolling mill 60. In FIG. 12, the “H” position is the home position of the traveling flash welding machine 20. The welding by the traveling flash welding machine 20 begins from the home position, and the welding terminates at the “A” position in the figure. After that, deburring by the deburring machine 30 begins from the “A” position, and the deburring terminates at the “B” position. FIG. 14 illustrates the conditions of deburring by the deburring machine 30. As illustrated in FIG. 14A, the vertical deburring cutter 31 descends toward the welded part, driven by the hydraulic cylinder 32, thereby removing the welding burrs on both left and right sides of the welded part. Then, as illustrated in FIG. 14B, the horizontal deburring cutter 33 travels in the horizontal direction toward the welded part, driven by the hydraulic cylinder 34, thereby removing the welding burrs from both top and bottom sides of the welded part.
According to the deburring by the deburring machine 30, there are problems of forming fins 3 at corners of the cross section of the welded part upon conducting deburring at the welded part using the vertical deburring cutter 31 or the horizontal deburring cutter 33, as shown in FIG. 14A and FIG. 14B, and giving fins 3, formed by deburring, left behind at corners of cross-section of the welded part of the billet 1, as shown in FIG. 14C. The presence of such fins, generates flaws in the succeeding rolling step, thus inducing deterioration of product quality and reducing the product yield in some cases.
There is another known deburring machine to remove welding burrs from the flash welded part, which is a rotary-blade type deburring machine, located at the downstream side of the traveling flash welding machine, to cut the welding burrs by pressing the rotating circular cutting edge against the welding burrs as disclosed in European Published Patent Application No. EP 1 057 563 A1. FIG. 15 illustrates a continuous rolling line provided with that type of deburring machine, and FIG. 16 shows a perspective view of a core part of that deburring machine.
As shown in FIG. 15, the rolling line arranges the heating furnace 10, the traveling flash welding machine 20, the deburring machine 40, and the rolling mill 60 in this sequential order. As seen in FIG. 16, the deburring machine 40 has cutting blades 41a and 41b, each having a rotating circular cutting edge. With the cutting blades 41a and 41b, the welding burr 2 formed on the top face of the welded part is removed. The cutting blades to remove the welding burrs on other faces of the welded part, (bottom face and right and left side faces) are also provided, though FIG. 16 does not show them.
According to thus structured rolling line, the leading end of the succeeding billet 1b delivered from the heating furnace 10 and the trailing end of the preceding billet 1a are welded to join together while traveling them using the traveling flash welding machine 20, and the welding burrs 2 formed on the welded part are removed by the deburring machine 40, and then thus formed endless billet 1 is continuously rolled by the rolling mill 60. In FIG. 15, the “H” position is the home position of the traveling flash welding machine 20. The welding by the traveling flash welding machine 20 begins from the home position, and the welding terminates at the “A” position in the figure. The welding burrs 2 at the welded part are removed while the billet 1 passes through the deburring machine 40. The deburring operation with that type of deburring machine 40 avoids the generation of fins 3 which raise a problem in deburring operation with the deburring machine 30, which is illustrated in FIGS. 12 to 14.
There are, however, problems in the deburring using the above deburring machine 40. That is, as illustrated in FIG. 17, when the continuously cast billet 1 is cut to a specified length in a continuous casting process using a mechanical diagonal cutter 71 equipped with a mobile cutting blade 72a and stationary cutting blade 72b, (FIG. 17A), the cut section deforms, (FIG. 17B). In this state, if the cross sections of the preceding billet 1a and the succeeding billet 1b are butted against each other, a significant misalignment 4 appears particularly at corners (edges) of the cross sections, (FIG. 17C). If flash welding is applied to these billets 1a and 1b, having that misalignment 4, (FIG. 17D), the portions near the misalignment 4 are not fully welded and result in a defect 6 caused by the misalignment 4 left behind at the welded part, (FIG. 17E). Since that type of defect 6 caused by the misalignment 4 cannot be removed by deburring (hatched part 5) by the deburring machine 40, (FIG. 17F), the defect 6 caused by the misalignment 4 is left behind at corners of the cross section of the billet 1 before rolling, (FIG. 17G). As a result, flaws appear in the succeeding rolling step, which may deteriorate the product quality and decrease the product yield.
As described above, the continuous roiling technology in the related art raises the problem that, when the welding burrs formed at the flash welded part are removed by a deburring machine, defects caused by fins or misalignment are left behind at corners of cross section at the welded part, which defects become flaws in the succeeding rolling step, thereby deteriorating the product quality and decreasing the product yield.
It would therefore be helpful to provide a continuous rolling method and a continuous rolling apparatus to attain good product quality and product yield by preventing the generation of flaws during rolling in the continuous rolling technology to manufacture steel rods, wires, and the like.